Yoga is everywhere among the affluent and the educated. The bending, stretching, and deep breathing have become a kind of oxygen for the modern soul, as a tour of the neighborhood shows rather quickly. New condo developments feature yoga studios as perks. Cruise ships tout the accomplishments of their yoga instructors, as do tropical resorts. Senior centers and children’s museums offer the stretching as a fringe benefit—Hey, parents, fitness can be fun. Hollywood stars and professional athletes swear by it. Doctors prescribe it for natural healing. Hospitals run beginner classes, as do many high schools and colleges. Clinical psychologists urge patients to try yoga for depression. Pregnant women do it (very carefully) as a form of prenatal care. The organizers of writing and painting workshops have their pupils do yoga to stir the creative spirit. So do acting schools. Musicians use it to calm down before going on stage.

Not to mention all the regular classes. In New York City, where I work, it seems like a yoga studio is doing business every few blocks. You can also take classes in Des Moines and Dushanbe, Tajikistan.

Once an esoteric practice of the few, yoga has transformed itself into a global phenomenon as well as a universal icon of serenity, one that resonates deeply with tense urbanites. In 2010, the city of Cambridge, Massachusetts, began illustrating its parking tickets with a series of calming yoga poses.

The popularity of yoga arises not only because of its talent for undoing stress but because its traditions make an engaging counterpoint to modern life. It’s unplugged and natural, old and centered—a kind of anti-civilization pill that can neutralize the dissipating influence of the Internet and the flood of information we all face. Its ancient serenity offers a new kind of solace.

An indication of yoga’s social ascendency is how its large centers often get housed in former churches, monasteries, and seminaries, the settings frequently rural and inspirational. Kripalu, on more than three hundred rolling acres of the Berkshires in western Massachusetts, was once a Jesuit seminary. Each year its yoga school graduates hundreds of new teachers. And they in turn produce thousands of new yogis and yoginis, or female yogis.

Even the White House is into yoga. Michelle Obama made it part of Let’s Move—her national program of exercise for children, which seeks to fight obesity. The First Lady talks about yoga on school visits and highlights the discipline at the annual Easter Egg Roll, the largest public event on the White House social calendar. Starting in 2009, the egg roll has repeatedly featured a Yoga Garden with colorful mats and helpful teachers. The sessions start early and go throughout the day.

On the White House lawn in 2010, an adult dressed as the Cat in the Hat—a character from the Dr. Seuss book—did a standing posture on one leg. A tougher demonstration featured five yogis simultaneously upending themselves in Headstands. At the 2011 event, the Easter Bunny did a tricky balancing pose. The children watched, played along, and took home a clear message about what the President and First Lady considered to be a smart way of getting in shape.

Yoga is one of the world’s fastest-growing health and fitness activities. The Yoga Health Foundation, based in California, puts the current number of practitioners in the United States at twenty million and around the globe at more than two hundred and fifty million. Many more people, it says, are interested in trying yoga. To spread the word, the foundation organizes Yoga Month—a celebration every September that blankets the United States with free yoga classes, activities, and health fairs.

By any measure, the activity is too widespread and its participants too affluent for advertisers and the news media to ignore. Health and beauty magazines do regular features. The New York Times, where I work, has run hundreds of articles and in 2010 began a regular column, Stretch. It has profiled everything from studios that offer hot yoga in overheated rooms to a gathering of thousands in Central Park that its organizers called the largest yoga class on record. A main attraction of that event was the corporate gifts. Participants got JetBlue yoga mats, SmartWater bottles, and ChicoBags filled with giveaways. The allure was so great that many people got stuck in entrance lines before a downpour chased everybody away.

Yoga may be in the air culturally. But it is also quite visibly a big business. Merchants sell mats, clothes, magazines, books, videos, travel junkets, creams, healing potions, shoes, soy snacks, and many accessories deemed vital to practice—as well as classes. Purists call it the yoga industrial complex. Increasingly, the big financial stakes have upended the traditional ethos. Bikram Choudhury, the founder of Bikram Yoga, a hot style, copyrighted his sequence of yoga poses and had his lawyers send out hundreds of threatening notices that charged small studios with violations. He is not alone. In the United States, yoga entrepreneurs have sought to enhance their exclusivity by registering thousands of patents, trademarks, and copyrights.

Market analysts identify yoga as part of a demographic known as LOHAS—for Lifestyles of Health and Sustainability. Its upscale, well-educated individuals are drawn to sustainable living and ecological initiatives. They drive hybrid cars, buy natural products, and seek healthy lifestyles. Yoga moms (a demographic successor to soccer moms) are an example. According to marketing studies, they tend to buy clothes for their children from such places as Mama’s Earth, its goods made from organic cotton, hemp, and recycled materials.

One factor that distinguishes modern yoga from its predecessors is its transformation from a calling into a premium lifestyle. Another is that women make up the vast majority of its practitioners, a fact that dramatically influences the nature of its marketplace. Women buy more books than men, read more, spend more on consumer goods, and pay more attention to their health and appearance.

Yoga Journal—the field’s leading magazine, founded in 1975—claims two million readers and identifies its audience as 87 percent women. It revels in their quality, citing high incomes, impressive jobs, and good educations. A brochure for prospective advertisers notes that more than 90 percent have gone to college.

The colorful pages of the magazine offer a vivid example of how companies target the demographic. Hundreds of ads promote skin-care products, sandals, jewelry, natural soaps, special vitamins and enzymes, alternative cures and therapies, smiling gurus, and ecofriendly cars. Each issue features an index to advertisers. One of my favorites is Hard Tail, a clothing line whose ads feature attractive women in striking poses. “Forever,” reads the minimalist copy.

Another is Lululemon Athletica, a hip brand of yoga clothing known for its form-fitting apparel, most especially its ability to shape and display the buttocks to best advantage. Recently, a market analyst identified Lulu’s signature item as the $98 Groove Pant, “cut with all kinds of special gussets and flat seams to create a snug gluteal enclosure of almost perfect globularity, like a drop of water.”

All of which bears on what yoga (as opposed to its accessories) does for the body and mind or, more precisely, on what gurus, spas, books, instructional videos, merchants, television shows, magazines, resorts, and health clubs say that it does.

In this regard, it is important to remember that yoga has no governing body. There’s no hierarchy of officials or organizations meant to ensure purity and adherence to agreed-upon sets of facts and poses, rules and procedures, outcomes and benefits. It’s not like a religion or modern medicine, where rigorous schooling, licensing, and boards seek to produce a high degree of conformity. And forget about government oversight. There’s no body such as the Consumer Product Safety Commission or the Food and Drug Administration to ensure that yoga lives up to its promises. Instead, it’s a free-for-all—and always has been. Over the ages, that freedom has resulted in a din of conflicting claims.

“The beginner,” notes I. K. Taimni, an Indian scholar, “is likely to feel repulsed by the confusion and exaggerated statements.” Taimni wrote that a half century ago. Today the situation is worse. For one thing, the explosion in publishing—print and electronic—has amplified the din into a cacophony. Another factor is the profit motive.

Billions of dollars are now at stake in public representations of what yoga can do, and the temptations are plentiful to lace declarations with everything from self-deception and happy imprecision to willful misrepresentations and shadings of the truth. Another temptation is to avoid any mention of damage or adverse consequences—a silence often rooted in economic rationalizations. Why tell the whole story if full disclosure might drive away customers? Why limit the sales appeal? Why not let the discipline be all things to all people?

Anyone who has done yoga for a while can rattle off a list of benefits. It calms and relaxes, eases and renews, energizes and strengthens. It somehow makes us feel better.

But beyond such basics lies a frothy hodgepodge of public claims and assurances, sales pitches and New Age promises. The topics include some of life’s most central aspirations—health, attractiveness, fitness, healing, sleep, safety, longevity, peace, willpower, control of body weight, happiness, love, knowledge, sexual satisfaction, personal growth, fulfillment, and the far boundaries of what it means to be human, not to mention enlightenment.

This book cuts through the confusion that surrounds modern yoga and describes what science tells us. It unravels more than a century’s worth of research to discern what’s real and what’s not, what helps and what hurts—and nearly as important, why. It casts light on yoga’s hidden workings as well as the disconcerting reality of false claims and dangerous omissions. At heart, it illuminates the risks and the rewards.

Many, it turns out, are unfamiliar.

I came to this book as a knowledgeable amateur. During my freshman year of college, in 1970, I got hooked on yoga because it felt good and seemed to make me healthier in body and mind. My first teacher said it was important to do some—even a little—every day. That’s always been my goal, despite the usual struggle with good intentions. Yoga has become a good friend to whom I turn no matter how crazy my life gets.

I began my research in 2006. My plan was simple. I’d track down the best science I could find and answer a lot of questions that I had accumulated over the decades, things I had wondered about but never had a chance to explore.

My first surprise was how yoga had morphed into a confusing array of styles and brands. I knew enough to understand that the origin of it all was Hatha yoga—the variety that centers on postures, breathing, and drills meant to strengthen the body and the mind (as opposed to the yogas of ethics and religious philosophy). Today, Hatha and its offspring are the most widely practiced forms of yoga on the planet, having produced scores of variations that range from local styles in most every country to such ubiquitous global brands as Iyengar and Ashtanga.

My enthusiasm for gyms and swimming also gave me a reasonable perspective on how yoga differs from regular exercise. In general (with exceptions we’ll study closely), it goes slow rather than fast, emphasizing static postures and fluid motions rather than the rapid, forceful repetitions of, say, spinning or running. Its low-impact nature puts less strain on the body than traditional sports, increasing its appeal for young people as well as aging boomers. In terms of physiology, it takes a minimalist approach to burning calories, contracting muscles, and stressing the body’s cardiovascular system. Perhaps most distinctively, it places great emphasis on controlling the breath and fostering an inner awareness of body position. Advanced yoga, in turn, goes further to encourage concentration on subtle energy flows. Overall, compared to sports and other forms of Western exercise, yoga draws the attention inward.

I began examining the yogic literature with a sense of wariness. Long ago, while working at the University of Wisconsin on a study of respiratory physiology, I came across a flat contradiction to one of modern yoga’s central tenets—that fast breathing floods the body and brain with revitalizing oxygen. In contrast, a textbook I was reading at the time said the pace of human respiration “can drop to one-half or rise to over one hundred times normal without appreciably influencing the amount of blood oxygenated.” I see now that, in 1975, I underlined that passage quite heavily.

Unfortunately, my survey lived up to my low expectations. Some books and authors shone brightly. (See Further Reading for a list.) But on the whole, I found the literature dull with dreaminess, assertions with no references, and a surprising number of obvious untruths. I wanted tips for tracking down good science but instead got a muddle. The writing, old and new, turned out to run toward the curiously dogmatic and, at best, to contain only a smattering of science. Much of it was similar to what Richard Feynman, a founder of modern physics, disparaged as cargo-cult science—that is, material that appears scientific but lacks factual integrity.

By contrast, my plunge into the scientific literature left me heartened. Federal officials at the National Institutes of Health in Bethesda, Maryland, run a wonderful electronic library of global medical reports known as PubMed, short for Public Medicine. It showed that scientists had written nearly one thousand papers related to yoga—the number rising in the early 1970s and soaring in recent years, with reports added every few days. The studies ranged from the flaky and superficial to the probing and rigorous. The authors included researchers at Princeton and Duke, Harvard and Columbia. Moreover, the field had gone global. Scientists in Sweden and Hong Kong were publishing serious papers.

But the closer I looked, the more I judged this body of information to be rather limited. Some general topics had been covered fairly well—for instance, how yoga can relax and heal. But many others were ignored, and much of the published science turned out to be superficial. For instance, studies for the approval of a new drug can require the participation of hundreds or even thousands of human subjects, the large numbers increasing the reliability of the findings. In contrast, many yoga investigations had fewer than a dozen participants. Some featured just one individual.

The superficiality turned out to have fairly obvious roots. Research on yoga was often a hobby or a sideline. It had no big corporate sponsors (there being no hope of discoveries that could lead to expensive pills or medical devices) and relatively little financial support from governments. Federal centers tend to specialize in advanced kinds of esoteric research as well as pressing issues of public health, with their investigations typically carried out at institutes and universities. In short, modern science seemed to care little.

The exception turned out to be areas where yoga intersected other disciplines or made bold claims strongly at odds with the conventional wisdom. Such crossroads proved to be scientifically rich. For instance, scientists interested in sports medicine and exercise physiology had lavished attention on yoga’s fitness claims. So, too, physicians had zeroed in on yoga’s reputation for safety.

The limitations of the current literature sent me casting a wide net, and I immediately made a big catch. It was a very old book—A Treatise on the Yoga Philosophy—written by a young Indian doctor and published in 1851 in Benares (now known as Varanasi), the ancient city on the Ganges that marks the spiritual heart of Hinduism. It came to my attention because a few Western scholars had referred to it in passing.

I got lucky and found that Google Books had recently scanned Harvard’s copy into its electronic archive, so I was able to download the whole thing in a flash. Its language was archaic. But the author had addressed the science of yoga with great skill, illuminating an important aspect of respiratory physiology that many authorities still get wrong today.

The book surprised me because I had been told that Indian research on yoga—though pioneering—was typically of poor quality. But I kept finding gems. A curious scientist, often working in India or born in India and doing research abroad, would address some riddle of yoga and make important finds. It happened not only with respiratory physiology but psychology, cardiology, endocrinology, and neurology. The scientists often acted with rigor, going against the day’s tide.

Intrigued, I traveled to India to learn more about these early investigators and eventually came to see them as a kind of intellectual vanguard. Their reports tended to predate the electronic archives of PubMed, making them all but invisible to modern researchers. But their findings turned out to be central to the field’s development.

As I widened my research, I had the great good fortune to sit at the feet of Mel Robin, a veteran yoga teacher and star of yoga science. Mel had worked at Bell Telephone Laboratories (the birthplace of the transistor, the heart of computer chips) for nearly three decades before turning to an investigation of yoga. His labor of love produced two massive books totaling nearly two thousand pages. What Mel did uniquely was roam far beyond the literature of yoga to show how the general discoveries of modern science bear on the discipline. His example encouraged the kind of independent thinking I had begun at the University of Wisconsin.

Over the years, the widening of my research brought me into contact not only with Mel but a wonderful variety of scientists, healers, yogis, medical doctors, mystics, federal officials, and other students of what science tells us about yoga. If science is the spine of this book, they are the flesh and blood.

My focus is practical. In places, the book touches on topics of Eastern spirituality—meditation and mindfulness, liberation and enlightenment—but makes no effort to explore them. Rather, it zeroes in relentlessly on what science tells us about postural yoga. I mean no disrespect to the Hindu religion or spiritual traditions that embrace the big picture. But if this book succeeds, it does so because it limits itself to a poorly known body of reductionist findings. Even so, I should note that I view the scientific process as limited and unable to answer the most important questions in life, as does any true believer. The epilogue explores what may lie beyond.

In the end, my examination revealed not only a wealth of findings but a remarkable lack of knowledge among yogis, gurus, and practitioners about the reports and investigations. This is pure speculation. But I’d be surprised if the community knows a hundredth or even a thousandth of what scientists have learned over a century and a half.

This book tells that story. In essence, it offers an impartial evaluation of an important social phenomenon that began to stir millennia ago. And if I may, it is the first to do so.

I have structured this book to start with issues of common interest and to end with topics that are less familiar. That flow, it turns out, parallels the development of scientific interest over the decades. So the book has a loose chronological organization.

The portrait of yoga that emerges is quite different in important respects from the usual claims. In some cases, the news is better.

For instance, a number of teachers credit yoga with powers of sexual renewal. The science not only confirms that claim but shows how specific poses can act as aphrodisiacs that produce surges of sex hormones and brain waves indistinguishable from those of lovers. More generally, recent clinical studies give substance to the idea that yoga can improve the sex lives of men and women, documenting how new practitioners report not only enhanced feelings of pleasure and satisfaction but emotional closeness with partners.

The health benefits also turn out to be considerable. While many gurus and how-to books praise yoga as a path to ultimate well-being, their descriptions are typically vague. Science nails the issue.

For example, recent studies indicate that yoga releases natural substances in the brain that act as strong antidepressants, suggesting great promise for the enhancement of personal health. Globally, depression cripples more than one hundred million people. Every year, its hopelessness results in nearly a million suicides.

Amy Weintraub, a major figure in this book, recounts how yoga saved her life by cutting through clouds of despondency.

But if some findings uplift, others contradict the onslaught of bold claims and proffered cures.

Take body weight—a topic of enormous sensitivity for anyone trying to look good. For decades, teachers of yoga have hailed the discipline as a great way to shed pounds. But it turns out that yoga works so well at reducing the body’s metabolic rate that—all things being equal—people who take up the practice will burn fewer calories, prompting them to gain weight and deposit new layers of fat. And for better or worse, scientists have found that the individuals most skilled at lowering their metabolisms are women. Of course, other aspects of yoga do fight pounds successfully. The discipline builds body awareness and its calming influence can help reduce stress eating. Most yoga teachers are lithe, not lumpy. But when yoga succeeds at weight control, the scientific evidence suggests that it does so in spite of—not because of—its basic impact on the human metabolism.

That’s one of yoga’s dirty little secrets. It turns out there are plenty of others, some quite significant.

Yoga has produced waves of injuries. Take strokes, which arise when clogged vessels divert blood from the brain. Doctors have found that certain poses can result in brain damage that turns practitioners into cripples with drooping eyelids and unresponsive limbs.

Darker still, some authorities warn of madness. As Carl Jung put it, advanced yoga can “let loose a flood of sufferings of which no sane person ever dreamed.” Many yoga books cite Jung approvingly but always seem to miss that quote. Even so, it represented his considered opinion after two decades of study and reflection.

Overall, the risks and benefits turned out to be far greater than anything I ever imagined. Yoga can kill and maim—or save your life and make you feel like a god. That’s quite a range. In comparison, it makes most other sports and exercises seem like child’s play.

My research has prompted me to change my own routine. I have deemphasized or dropped certain poses, added others, and in general now handle yoga with much greater care. I hope you benefit, too.

I see this book as similar to informed consent—the information that the subjects of medical experiments and novel treatments are given to make sure they understand the stakes, pro and con.

To me, the benefits unquestionably outweigh the risks. The discipline on balance does more good than harm. Still, yoga makes sense only if done intelligently so as to limit the degree of personal danger. I’m convinced that even modest precautions will avert waves of pain, remorse, grief, and disability.

The heroes of this book are the hundreds of scientists and physicians who toiled inconspicuously over the decades to uncover the truth despite the obstcenter1es of scarce funding and institutional apathy. Their early inquiries not only began the process of illuminating yoga but, as it turns out, produced a remarkable side effect. They helped transform the nature of the discipline.

Yoga at the start was an obscure cult steeped in magic and eroticism. At the end, it fixated on health and fitness.

To my surprise, it turned out that science played an important role in the modernization. As investigators began to show how the ostensible wonders of yoga had natural explanations, the discipline worked hard to reinvent itself. A new generation of gurus downplayed the rapturous and the miraculous for a focus on material well-being. In essence, they turned yoga on its head by elevating the physical over the spiritual, helping create the secular discipline now practiced around the globe.

The first chapter details this upheaval. The tale is important not only for revealing the origins of the health agenda but for introducing main characters and themes. For instance, it turns out that a number of yoga mircenter1es—if demonstrably untrue—nonetheless involve major alterations of physiology that can produce a wealth of real benefits. They can lift moods. They can fight heart disease. The newest research indicates that they may even slow the body’s biological clock.

Not that science has all the answers.

To the contrary, the investigation of the discipline began in response to an astonishing spectcenter1e nearly two centuries ago that still poses a number of fundamental questions today.

The science of yoga does more than reveal secrets. It can also shed light on real mysteries.

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Prologue

Yoga is everywhere among the affluent and the educated. The bending, stretching, and deep breathing have become a kind of oxygen for the modern soul, as a tour of the neighborhood shows rather quickly. New condo developments feature yoga studios as perks. Cruise ships tout the accomplishments of their yoga instructors, as do tropical resorts. Senior centers and children’s museums offer the stretching as a fringe benefit—Hey, parents, fitness can be fun. Hollywood stars and professional athletes swear by it. Doctors prescribe it for natural healing. Hospitals run beginner classes, as do many high schools and colleges. Clinical psychologists urge patients to try yoga for depression. Pregnant women do it (very carefully) as a form of prenatal care. The organizers of writing and painting workshops have their pupils do yoga to stir the creative spirit. So do acting schools. Musicians use it to calm down before going on stage.

Not to mention all the regular classes. In New York City, where I work, it seems like a yoga studio is doing business every few blocks. You can also take classes in Des Moines and Dushanbe, Tajikistan.

Once an esoteric practice of the few, yoga has transformed itself into a global phenomenon as well as a universal icon of serenity, one that resonates deeply with tense urbanites. In 2010, the city of Cambridge, Massachusetts, began illustrating its parking tickets with a series of calming yoga poses.

The popularity of yoga arises not only because of its talent for undoing stress but because its traditions make an engaging counterpoint to modern life. It’s unplugged and natural, old and centered—a kind of anti-civilization pill that can neutralize the dissipating influence of the Internet and the flood of information we all face. Its ancient serenity offers a new kind of solace.

An indication of yoga’s social ascendency is how its large centers often get housed in former churches, monasteries, and seminaries, the settings frequently rural and inspirational. Kripalu, on more than three hundred rolling acres of the Berkshires in western Massachusetts, was once a Jesuit seminary. Each year its yoga school graduates hundreds of new teachers. And they in turn produce thousands of new yogis and yoginis, or female yogis.

Even the White House is into yoga. Michelle Obama made it part of Let’s Move—her national program of exercise for children, which seeks to fight obesity. The First Lady talks about yoga on school visits and highlights the discipline at the annual Easter Egg Roll, the largest public event on the White House social calendar. Starting in 2009, the egg roll has repeatedly featured a Yoga Garden with colorful mats and helpful teachers. The sessions start early and go throughout the day.

On the White House lawn in 2010, an adult dressed as the Cat in the Hat—a character from the Dr. Seuss book—did a standing posture on one leg. A tougher demonstration featured five yogis simultaneously upending themselves in Headstands. At the 2011 event, the Easter Bunny did a tricky balancing pose. The children watched, played along, and took home a clear message about what the President and First Lady considered to be a smart way of getting in shape.

Yoga is one of the world’s fastest-growing health and fitness activities. The Yoga Health Foundation, based in California, puts the current number of practitioners in the United States at twenty million and around the globe at more than two hundred and fifty million. Many more people, it says, are interested in trying yoga. To spread the word, the foundation organizes Yoga Month—a celebration every September that blankets the United States with free yoga classes, activities, and health fairs.

By any measure, the activity is too widespread and its participants too affluent for advertisers and the news media to ignore. Health and beauty magazines do regular features. The New York Times, where I work, has run hundreds of articles and in 2010 began a regular column, Stretch. It has profiled everything from studios that offer hot yoga in overheated rooms to a gathering of thousands in Central Park that its organizers called the largest yoga class on record. A main attraction of that event was the corporate gifts. Participants got JetBlue yoga mats, SmartWater bottles, and ChicoBags filled with giveaways. The allure was so great that many people got stuck in entrance lines before a downpour chased everybody away.

Yoga may be in the air culturally. But it is also quite visibly a big business. Merchants sell mats, clothes, magazines, books, videos, travel junkets, creams, healing potions, shoes, soy snacks, and many accessories deemed vital to practice—as well as classes. Purists call it the yoga industrial complex. Increasingly, the big financial stakes have upended the traditional ethos. Bikram Choudhury, the founder of Bikram Yoga, a hot style, copyrighted his sequence of yoga poses and had his lawyers send out hundreds of threatening notices that charged small studios with violations. He is not alone. In the United States, yoga entrepreneurs have sought to enhance their exclusivity by registering thousands of patents, trademarks, and copyrights.

Market analysts identify yoga as part of a demographic known as LOHAS—for Lifestyles of Health and Sustainability. Its upscale, well-educated individuals are drawn to sustainable living and ecological initiatives. They drive hybrid cars, buy natural products, and seek healthy lifestyles. Yoga moms (a demographic successor to soccer moms) are an example. According to marketing studies, they tend to buy clothes for their children from such places as Mama’s Earth, its goods made from organic cotton, hemp, and recycled materials.

One factor that distinguishes modern yoga from its predecessors is its transformation from a calling into a premium lifestyle. Another is that women make up the vast majority of its practitioners, a fact that dramatically influences the nature of its marketplace. Women buy more books than men, read more, spend more on consumer goods, and pay more attention to their health and appearance.

Yoga Journal—the field’s leading magazine, founded in 1975—claims two million readers and identifies its audience as 87 percent women. It revels in their quality, citing high incomes, impressive jobs, and good educations. A brochure for prospective advertisers notes that more than 90 percent have gone to college.

The colorful pages of the magazine offer a vivid example of how companies target the demographic. Hundreds of ads promote skin-care products, sandals, jewelry, natural soaps, special vitamins and enzymes, alternative cures and therapies, smiling gurus, and ecofriendly cars. Each issue features an index to advertisers. One of my favorites is Hard Tail, a clothing line whose ads feature attractive women in striking poses. “Forever,” reads the minimalist copy.

Another is Lululemon Athletica, a hip brand of yoga clothing known for its form-fitting apparel, most especially its ability to shape and display the buttocks to best advantage. Recently, a market analyst identified Lulu’s signature item as the $98 Groove Pant, “cut with all kinds of special gussets and flat seams to create a snug gluteal enclosure of almost perfect globularity, like a drop of water.”

All of which bears on what yoga (as opposed to its accessories) does for the body and mind or, more precisely, on what gurus, spas, books, instructional videos, merchants, television shows, magazines, resorts, and health clubs say that it does.

In this regard, it is important to remember that yoga has no governing body. There’s no hierarchy of officials or organizations meant to ensure purity and adherence to agreed-upon sets of facts and poses, rules and procedures, outcomes and benefits. It’s not like a religion or modern medicine, where rigorous schooling, licensing, and boards seek to produce a high degree of conformity. And forget about government oversight. There’s no body such as the Consumer Product Safety Commission or the Food and Drug Administration to ensure that yoga lives up to its promises. Instead, it’s a free-for-all—and always has been. Over the ages, that freedom has resulted in a din of conflicting claims.

“The beginner,” notes I. K. Taimni, an Indian scholar, “is likely to feel repulsed by the confusion and exaggerated statements.” Taimni wrote that a half century ago. Today the situation is worse. For one thing, the explosion in publishing—print and electronic—has amplified the din into a cacophony. Another factor is the profit motive.

Billions of dollars are now at stake in public representations of what yoga can do, and the temptations are plentiful to lace declarations with everything from self-deception and happy imprecision to willful misrepresentations and shadings of the truth. Another temptation is to avoid any mention of damage or adverse consequences—a silence often rooted in economic rationalizations. Why tell the whole story if full disclosure might drive away customers? Why limit the sales appeal? Why not let the discipline be all things to all people?

Anyone who has done yoga for a while can rattle off a list of benefits. It calms and relaxes, eases and renews, energizes and strengthens. It somehow makes us feel better.

But beyond such basics lies a frothy hodgepodge of public claims and assurances, sales pitches and New Age promises. The topics include some of life’s most central aspirations—health, attractiveness, fitness, healing, sleep, safety, longevity, peace, willpower, control of body weight, happiness, love, knowledge, sexual satisfaction, personal growth, fulfillment, and the far boundaries of what it means to be human, not to mention enlightenment.

This book cuts through the confusion that surrounds modern yoga and describes what science tells us. It unravels more than a century’s worth of research to discern what’s real and what’s not, what helps and what hurts—and nearly as important, why. It casts light on yoga’s hidden workings as well as the disconcerting reality of false claims and dangerous omissions. At heart, it illuminates the risks and the rewards.

Many, it turns out, are unfamiliar.

I came to this book as a knowledgeable amateur. During my freshman year of college, in 1970, I got hooked on yoga because it felt good and seemed to make me healthier in body and mind. My first teacher said it was important to do some—even a little—every day. That’s always been my goal, despite the usual struggle with good intentions. Yoga has become a good friend to whom I turn no matter how crazy my life gets.

I began my research in 2006. My plan was simple. I’d track down the best science I could find and answer a lot of questions that I had accumulated over the decades, things I had wondered about but never had a chance to explore.

My first surprise was how yoga had morphed into a confusing array of styles and brands. I knew enough to understand that the origin of it all was Hatha yoga—the variety that centers on postures, breathing, and drills meant to strengthen the body and the mind (as opposed to the yogas of ethics and religious philosophy). Today, Hatha and its offspring are the most widely practiced forms of yoga on the planet, having produced scores of variations that range from local styles in most every country to such ubiquitous global brands as Iyengar and Ashtanga.

My enthusiasm for gyms and swimming also gave me a reasonable perspective on how yoga differs from regular exercise. In general (with exceptions we’ll study closely), it goes slow rather than fast, emphasizing static postures and fluid motions rather than the rapid, forceful repetitions of, say, spinning or running. Its low-impact nature puts less strain on the body than traditional sports, increasing its appeal for young people as well as aging boomers. In terms of physiology, it takes a minimalist approach to burning calories, contracting muscles, and stressing the body’s cardiovascular system. Perhaps most distinctively, it places great emphasis on controlling the breath and fostering an inner awareness of body position. Advanced yoga, in turn, goes further to encourage concentration on subtle energy flows. Overall, compared to sports and other forms of Western exercise, yoga draws the attention inward.

I began examining the yogic literature with a sense of wariness. Long ago, while working at the University of Wisconsin on a study of respiratory physiology, I came across a flat contradiction to one of modern yoga’s central tenets—that fast breathing floods the body and brain with revitalizing oxygen. In contrast, a textbook I was reading at the time said the pace of human respiration “can drop to one-half or rise to over one hundred times normal without appreciably influencing the amount of blood oxygenated.” I see now that, in 1975, I underlined that passage quite heavily.

Unfortunately, my survey lived up to my low expectations. Some books and authors shone brightly. (See Further Reading for a list.) But on the whole, I found the literature dull with dreaminess, assertions with no references, and a surprising number of obvious untruths. I wanted tips for tracking down good science but instead got a muddle. The writing, old and new, turned out to run toward the curiously dogmatic and, at best, to contain only a smattering of science. Much of it was similar to what Richard Feynman, a founder of modern physics, disparaged as cargo-cult science—that is, material that appears scientific but lacks factual integrity.

By contrast, my plunge into the scientific literature left me heartened. Federal officials at the National Institutes of Health in Bethesda, Maryland, run a wonderful electronic library of global medical reports known as PubMed, short for Public Medicine. It showed that scientists had written nearly one thousand papers related to yoga—the number rising in the early 1970s and soaring in recent years, with reports added every few days. The studies ranged from the flaky and superficial to the probing and rigorous. The authors included researchers at Princeton and Duke, Harvard and Columbia. Moreover, the field had gone global. Scientists in Sweden and Hong Kong were publishing serious papers.

But the closer I looked, the more I judged this body of information to be rather limited. Some general topics had been covered fairly well—for instance, how yoga can relax and heal. But many others were ignored, and much of the published science turned out to be superficial. For instance, studies for the approval of a new drug can require the participation of hundreds or even thousands of human subjects, the large numbers increasing the reliability of the findings. In contrast, many yoga investigations had fewer than a dozen participants. Some featured just one individual.

The superficiality turned out to have fairly obvious roots. Research on yoga was often a hobby or a sideline. It had no big corporate sponsors (there being no hope of discoveries that could lead to expensive pills or medical devices) and relatively little financial support from governments. Federal centers tend to specialize in advanced kinds of esoteric research as well as pressing issues of public health, with their investigations typically carried out at institutes and universities. In short, modern science seemed to care little.

The exception turned out to be areas where yoga intersected other disciplines or made bold claims strongly at odds with the conventional wisdom. Such crossroads proved to be scientifically rich. For instance, scientists interested in sports medicine and exercise physiology had lavished attention on yoga’s fitness claims. So, too, physicians had zeroed in on yoga’s reputation for safety.

The limitations of the current literature sent me casting a wide net, and I immediately made a big catch. It was a very old book—A Treatise on the Yoga Philosophy—written by a young Indian doctor and published in 1851 in Benares (now known as Varanasi), the ancient city on the Ganges that marks the spiritual heart of Hinduism. It came to my attention because a few Western scholars had referred to it in passing.

I got lucky and found that Google Books had recently scanned Harvard’s copy into its electronic archive, so I was able to download the whole thing in a flash. Its language was archaic. But the author had addressed the science of yoga with great skill, illuminating an important aspect of respiratory physiology that many authorities still get wrong today.

The book surprised me because I had been told that Indian research on yoga—though pioneering—was typically of poor quality. But I kept finding gems. A curious scientist, often working in India or born in India and doing research abroad, would address some riddle of yoga and make important finds. It happened not only with respiratory physiology but psychology, cardiology, endocrinology, and neurology. The scientists often acted with rigor, going against the day’s tide.

Intrigued, I traveled to India to learn more about these early investigators and eventually came to see them as a kind of intellectual vanguard. Their reports tended to predate the electronic archives of PubMed, making them all but invisible to modern researchers. But their findings turned out to be central to the field’s development.

As I widened my research, I had the great good fortune to sit at the feet of Mel Robin, a veteran yoga teacher and star of yoga science. Mel had worked at Bell Telephone Laboratories (the birthplace of the transistor, the heart of computer chips) for nearly three decades before turning to an investigation of yoga. His labor of love produced two massive books totaling nearly two thousand pages. What Mel did uniquely was roam far beyond the literature of yoga to show how the general discoveries of modern science bear on the discipline. His example encouraged the kind of independent thinking I had begun at the University of Wisconsin.

Over the years, the widening of my research brought me into contact not only with Mel but a wonderful variety of scientists, healers, yogis, medical doctors, mystics, federal officials, and other students of what science tells us about yoga. If science is the spine of this book, they are the flesh and blood.

My focus is practical. In places, the book touches on topics of Eastern spirituality—meditation and mindfulness, liberation and enlightenment—but makes no effort to explore them. Rather, it zeroes in relentlessly on what science tells us about postural yoga. I mean no disrespect to the Hindu religion or spiritual traditions that embrace the big picture. But if this book succeeds, it does so because it limits itself to a poorly known body of reductionist findings. Even so, I should note that I view the scientific process as limited and unable to answer the most important questions in life, as does any true believer. The epilogue explores what may lie beyond.

In the end, my examination revealed not only a wealth of findings but a remarkable lack of knowledge among yogis, gurus, and practitioners about the reports and investigations. This is pure speculation. But I’d be surprised if the community knows a hundredth or even a thousandth of what scientists have learned over a century and a half.

This book tells that story. In essence, it offers an impartial evaluation of an important social phenomenon that began to stir millennia ago. And if I may, it is the first to do so.

I have structured this book to start with issues of common interest and to end with topics that are less familiar. That flow, it turns out, parallels the development of scientific interest over the decades. So the book has a loose chronological organization.

The portrait of yoga that emerges is quite different in important respects from the usual claims. In some cases, the news is better.

For instance, a number of teachers credit yoga with powers of sexual renewal. The science not only confirms that claim but shows how specific poses can act as aphrodisiacs that produce surges of sex hormones and brain waves indistinguishable from those of lovers. More generally, recent clinical studies give substance to the idea that yoga can improve the sex lives of men and women, documenting how new practitioners report not only enhanced feelings of pleasure and satisfaction but emotional closeness with partners.

The health benefits also turn out to be considerable. While many gurus and how-to books praise yoga as a path to ultimate well-being, their descriptions are typically vague. Science nails the issue.

For example, recent studies indicate that yoga releases natural substances in the brain that act as strong antidepressants, suggesting great promise for the enhancement of personal health. Globally, depression cripples more than one hundred million people. Every year, its hopelessness results in nearly a million suicides.

Amy Weintraub, a major figure in this book, recounts how yoga saved her life by cutting through clouds of despondency.

But if some findings uplift, others contradict the onslaught of bold claims and proffered cures.

Take body weight—a topic of enormous sensitivity for anyone trying to look good. For decades, teachers of yoga have hailed the discipline as a great way to shed pounds. But it turns out that yoga works so well at reducing the body’s metabolic rate that—all things being equal—people who take up the practice will burn fewer calories, prompting them to gain weight and deposit new layers of fat. And for better or worse, scientists have found that the individuals most skilled at lowering their metabolisms are women. Of course, other aspects of yoga do fight pounds successfully. The discipline builds body awareness and its calming influence can help reduce stress eating. Most yoga teachers are lithe, not lumpy. But when yoga succeeds at weight control, the scientific evidence suggests that it does so in spite of—not because of—its basic impact on the human metabolism.

That’s one of yoga’s dirty little secrets. It turns out there are plenty of others, some quite significant.

Yoga has produced waves of injuries. Take strokes, which arise when clogged vessels divert blood from the brain. Doctors have found that certain poses can result in brain damage that turns practitioners into cripples with drooping eyelids and unresponsive limbs.

Darker still, some authorities warn of madness. As Carl Jung put it, advanced yoga can “let loose a flood of sufferings of which no sane person ever dreamed.” Many yoga books cite Jung approvingly but always seem to miss that quote. Even so, it represented his considered opinion after two decades of study and reflection.

Overall, the risks and benefits turned out to be far greater than anything I ever imagined. Yoga can kill and maim—or save your life and make you feel like a god. That’s quite a range. In comparison, it makes most other sports and exercises seem like child’s play.

My research has prompted me to change my own routine. I have deemphasized or dropped certain poses, added others, and in general now handle yoga with much greater care. I hope you benefit, too.

I see this book as similar to informed consent—the information that the subjects of medical experiments and novel treatments are given to make sure they understand the stakes, pro and con.

To me, the benefits unquestionably outweigh the risks. The discipline on balance does more good than harm. Still, yoga makes sense only if done intelligently so as to limit the degree of personal danger. I’m convinced that even modest precautions will avert waves of pain, remorse, grief, and disability.

The heroes of this book are the hundreds of scientists and physicians who toiled inconspicuously over the decades to uncover the truth despite the obstcenter1es of scarce funding and institutional apathy. Their early inquiries not only began the process of illuminating yoga but, as it turns out, produced a remarkable side effect. They helped transform the nature of the discipline.

Yoga at the start was an obscure cult steeped in magic and eroticism. At the end, it fixated on health and fitness.

To my surprise, it turned out that science played an important role in the modernization. As investigators began to show how the ostensible wonders of yoga had natural explanations, the discipline worked hard to reinvent itself. A new generation of gurus downplayed the rapturous and the miraculous for a focus on material well-being. In essence, they turned yoga on its head by elevating the physical over the spiritual, helping create the secular discipline now practiced around the globe.

The first chapter details this upheaval. The tale is important not only for revealing the origins of the health agenda but for introducing main characters and themes. For instance, it turns out that a number of yoga mircenter1es—if demonstrably untrue—nonetheless involve major alterations of physiology that can produce a wealth of real benefits. They can lift moods. They can fight heart disease. The newest research indicates that they may even slow the body’s biological clock.

Not that science has all the answers.

To the contrary, the investigation of the discipline began in response to an astonishing spectcenter1e nearly two centuries ago that still poses a number of fundamental questions today.

The science of yoga does more than reveal secrets. It can also shed light on real mysteries.

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The Risks and the Rewards

The Science of Yoga

The Risks and the Rewards

The Science of Yoga draws on more than a century of painstaking research to present the first impartial evaluation of a practice thousands of years old. It celebrates what’s real and shows what’s illusory, describes what’s uplifting and beneficial and what’s flaky and dangerous—and why. Broad unveils a burgeoning global industry that attracts not only curious scientists but true believers and charismatic hustlers. He shatters myths, lays out unexpected benefits, and offers a compelling vision of how the ancient practice can be improved.

The Health Benefits of Yoga

Praise

"Yoga, an ancient practice with millions of modern practitioners, has been the subject of overheated speculation and grandiose claims; it has been dismissed without warrant as well, underappreciated by some who might well benefit from it. The Science of Yoga is a lucid and long overdue account of what scientists have found in their attempts to ferret out the truth about what yoga can and cannot do to heal and make better the body and mind. It is a fascinating and important book."

"Yoga, an ancient practice with millions of modern practitioners, has been the subject of overheated speculation and grandiose claims; it has been dismissed without warrant as well, underappreciated by some who might well benefit from it. The Science of Yoga is a lucid and long overdue account of what scientists have found in their attempts to ferret out the truth about what yoga can and cannot do to heal and make better the body and mind. It is a fascinating and important book."

"The Science of Yoga offers a riveting, much-needed, clear-eyed look at the yoga mystique. In this investigation, science journalist William Broad pulls back the curtain on the little-discussed world of yoga injuries and risks, while setting the record straight about the numerous potential benefits. Downward dog will never look the same. "

– Daniel Goleman, author of Emotional Intelligence

"If this book doesn’t motivate you to practice yoga, nothing will. Broad sheds light on yoga’s health benefits and hoaxes, covering everything from headstands to hypertension, the vagus nerve to the YogaButt. Finally I understand why I feel so good when I do yoga. His lively exploration of its evolution from Benares to Beverly Hills flows like any great practice should -- with intelligence, good humor and some mindblowing insights.--Priscilla Warner, author of Learning to Breathe"

– My Yearlong Quest to Bring Calm to My Life and co-author of The Faith Club

"After reading The Science of Yoga, I am even more awed by the magnificent complexities of the human body and mind, and astonished that we can exert so much control over this invisible realm through the practice of yoga. Broad has not only thoroughly researched his topic, he has lived it."

– Alan Lightman, author of Einstein’s Dreams

"William Broad is optimistic and hopeful in pointing the way to its future as a major force in preventing and treating disease. "

– Gail Sheehy, author of Passages in Caregiving

"In this compelling work of investigative journalism, William Broad exposes the scientific claims made about yoga--from its much-vaunted healing powers to yogasms--to scientific scrutiny. The Science of Yoga is a wonderful read that any yoga practitioner thirsting for authenticity should study carefully before suiting up."

– David Gordon White, author of Kiss of the Yogini

"Dramatic...a flair for provocation…valuable. "

– Publishers Weekly

Read an Excerpt

The Science of Yoga

The Risks and the Rewards

By William J Broad

Excerpts

Prologue

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About the Author

William J. Broad has practiced yoga since 1970. A bestselling author and senior writer at The New York Times, he has won every major award in print and television during more than thirty years as a science journalist. With New York Times colleagues, he has twice won the Pulitzer Prize, as well as an Emmy Award and a DuPont. He is the author or coauthor of seven books, including Germs: Biological Weapons and America’s Secret War, a #1 New York Times bestseller.